Electron discharge device



March 5, 1957 B. E. BARNES ELECTRON DISCHARGE DEVICE Filed Oct. 21, 1953 5 6 4 2 B w v a A w mv M a H l 4 o M E M O 6 o 4 m M 4.4-U 2 m m m I L L INVENTOR.

BRYCE E BARNES BY 6 fiw v Arrokms ELECTRON DISCHARGE DEVICE Bryce E. Barnes, Edina, Minm, assignor to Minneapolis- Honeywell Regulator Company, Minneapolis,- Mind, a corporation of Delaware Application October 21, 1953, Serial No. 387,389

3 Claims. (Cl. 313'266) This invention relates to electron discharge devices such as those of the grid controlled discharge type and more particularly to improvements in the structure of such devices.

In modern electronic equipment, and especially in electronic control systems, the equipment must he made to withstand severe vibration, shock and relatively high temperatures, because of the conditions under which it must operate. It has been found that the weakest portion of such a system is often the vacuum tubes, which under conditions of continued vibration often develop intere'lectrode shorts and failures. A disadvantage of the usual grid structure in a tube is that in addition to the tendency toward interelectrode shorts, the grid has a resonant frequency usually quite low in the audio range which causes m'icrophonics and other undesirable signals to be introduced into the control system. In this invention the grid is maintained under relatively constant tension, even at operating temperatures, to prevent interelectrode shorts between the grid and other elements and also to increase the resonant frequency of the grid wires to a point where the vibrations are no longer a nuisance in the control system. A ceramic envelope is used to provide compactness, greater physical strength, and to allow operation at higher temperatures. a

It is an object of this invention, therefore, to provide an improved electron discharge device designed to withstand severe vibration under operating conditions without failure, and to handle a relatively large power output.

Another object of this invention is toprovide in an improved electron discharge device a taut grid which is maintained at relatively constant tension under all operating conditions.

Another object of the invention is to provide an improved electron discharge device having a ceramic envelope and having a grid which is maintained taut under all conditions ofi operation.

These and other features and advantages of this invention will bemore apparent from the following detailed description when considered with the accompanying drawings:

Figure l is a greatly eulargedview in cross-section of an electron discharge device of this invention illustrating the relationship between the parts comprising the device;

Figure 2 is the side elevation view of the discharge device used as an illustrative embodiment of this invention;

Figure 3 is a view of the interior of the lower section of the device and the associated electrodes, and

Figure 4 is a view of the interior of the upper section of the device.

Referring now to Figure 1 of the drawing, an electron tube is illustrated in which the envelope is constructed of two sections of ceramic. This ceramic may be of any suitable ceramic type material such as the zircon type or alumina type ceramics commercially available. In one successful embodiment of the tube a zircon type ceramic Alsimag 475 was used. A base section of the envenited States Patent no t. 2,784,337 C Patented Mar. 5, 1957 lope has a main portion in the shape of a disc which has two parallel ridges 11 and 12 elevated from the top surface thereof. Two shoulders 13 and 14 located adjacent the ridges 11 and 12 are also elevated above the surface of the disc. An upper section 15 of the envelope is cylindrical in shape with a diameter equal to that of the disc of lower section, and has a top wall 16. A lip 17 around the edge of the upper section is made to mate with and be sealed to the base section in a manner to be described. A pair of shoulders 20 and 21 which protlude from the inner wall of the cylinder are aligned with and approach but do not touch the shoulders 13 and M of the base section when the two sections are assembled.

The two ceramic sections are sealed together preferably by using known techniques of metallizing the surfaces of the ceramic to be joined. In one such process the surfaces to be metallized are coated with a tine molybdenum powder which is then fired athigh temperature to sinter the metal powder to the ceramic surface. These metallized surfaces of the ceramic may then be brazed together with silver solder or the like, forming a vacuum tight seal.

The tube has been illustrated as a triode having a cathode 22, a grid 23 and an anode 24. The anode 24, which has a planar collecting surface is constructed of a block of metal having good electrical and thermal conductivity, preferably copper, and is mounted in an ape; ture 25 in the upper section 15'. The edge of the aperture 25 is metallized and one end of a cylindrical metallic sleeve 26 is brazed therein. The opposite end of the sleeve 26 is brazed to the anode 24, thus forming a vacuum tight seal between anode and envelope while elimihating the difficulty in sealing which would otherwise be encountered due to different coeflicients of expansion between the ceramic envelope and the metal anode. The grid 23 of this device comprises a plurality of parallel spaced wires, which may be made of gold plated tungsten wire or other suitable material. The ends of the wires are brazed to a pair of L-shaped springs 30 and 31 which may be made of molybdenum. The grid wires are stretched across the two parallel ridges 11 and 12 which establish the plane of the grid and the L-shaped springs 30 and 31 rest on the shoulders 13 and 14 respectively. When the two sections of the envelope are assembled the shoulders 20 and 21 of the upper section compress the springs thus applying a continuous and relatively constant tension to the grid wires.

In the production of this type tube it is necessary that the tension applied to the grid of each tube produced be essentially equal, and it is also desirable in order that the ceramic envelope be easily produced that it need not conform to accurate tolerances, especially in the area of the shoulders. In order to avoid the difference in tension which would normally arise from differences in the spacing between shoulders of various tubes the springs are so constructed that as the ceramic parts are assembled the elastic limit of the spring is exceeded and the spring is slightly deformed. Since the springs are all made alike the exceeding of the elastic limit during assembly assures that the magnitude of the tension applied to the grid of each tube is essentially equal.

This tension on the grid wires serves a twofold purpose; first the relatively constant tension assures that the wires are always taut so that the spacing between electrodes will not change, due to sagging of the grid wires, which often occurs when the devices become heated and the wires expand. The second purpose the tensioning of the grid wires serves is to increase the resonant frequency at which the wires oscillate, and by raising the resonant frequency toward the upper end of the audible band, the microphonics and other undesirable signals introduced into the control system due to the grid arenas? vibration are also increased in frequency to the point Where they no longer effect the control system.

The cathode and filament assembly 19 comprises a cathode 22 having :a planar emitting surface, and is prefcrably of the matrix design described in the copending applications of Edward F. Rexer Serial Number 387,537 and John N. Dempsey Serial Number 387,515, both for Electron Emitting Cathodes, filed of even date herewith. The filament wire 32 is insulated with aluminum oxide 33 or similar insulating material and the entire filament area is potted with the insulating material, to prevent any vibration of the filament wires which often causes filament failure. The cathode and filament which are fastened together are held in position by a pair of substantially U-shaped supporting members 34, one of which is shown in Figure l. The ends of each supporting member are fastened to the corners of the cathode assembly and the centers of the supporting members are spot welded or otherwise fastened to a metal pin 35 which extends through the base of the device, The supporting members also provide an electrical connection from the cathode to the pin 35. A sleeve 36 is bnazed into in the tube base and the pin 35 which fits in the sleeve is adjusted for the proper cathode-grid spacing prior to brazing the pin to the sleeve. The ridges 11 and 12 serve as a reference plane from which the cathode-grid spacing is determined and by placing a suitable jig against the ridges the cathode may be quickly and accurately positioned to the proper setting. Three other pins 40, 41 and 42 which are connected to the filament 32 and grid 23 are brazed into metallized holes 43 in the ceramic base. The metallizing material is shown in Figure l as having a relatively thick cross section for purposes of illustration. In actual practice the thickness of the metallizing material on the ceramic may normally be in the order of .002 inch.

Pin 42 is connected to the grid 23 as follows. The metallizing of hole 43 is continued up onto a section of shoulder 14 and ridge 12. The L-shaped spring 31 is forced against the metallized ridge and shoulder section by the spring tension and this pressure type contact makes a good electrical path between the grid and the pin 42.

The device is evacuated through .a metal tube 44 which is brazed into a hole 46 drilled axially into the anode 24 and the hole 46 is met by a hole 47 drilled radially into the anode as is shown in Figure 1. When the evacuating is complete the metal tube end is pinched and sealed. A heat dissipating cap 45, having cooling fins, is fastened to the external portion of the anode as shown in Figure 2 after evacuation tube 44 has been pinched oif and sealed. The cap makes electrical contact with the anode and is used as the anode connection.

Figure 3 is a view looking down on the lower section v of the device and illustrates the preferred shape of the grid 23 and the cathode 22. The terminals 50 and 51 of the filament winding are shown connected to pins 40 and 41 by spot welding or other suitable means.

Figure 4 is a view looking up into the upper section of the envelope and illustrates the planar portion of the anode 24, the shape of the shoulders 20 and 21 and Cit the circular lip 17. The use of a ceramic envelope allows the construction of a very compact tube which can operate successfully at substantially higher temperatures than is possible with :a glass envelope. One successful embodiment of the tube is A" in diameter and 1" high, and has electrical characteristics which are similar to a medium-mu triode such as the 6SN7. The relatively high temperatures at which the tube can operate allows a substantially higher power dissipation, however, within the tube.

Many changes and modifications of this invention will undoubtedly occur to those who are skilled in the art and I therefore wish it understood that I intend to be limited by the scope of the appended claims and not by the specific embodiment of my invention which is disclosed herein for the purpose of illustration only.

i claim as my invention:

1. An electron discharge device comprising an envelope having an upper and a lower section of ceramic, bonding means uniting said sections together, an anode, a cathode, and a control electrode, said control electrode comprising a plurality of spaced wires, a pair of parallel ceramic ridges extending above the surface of said lower section, over which said control electrode is positioned, said ridges providing a reference surface and support for said control electrode, and means supporting said anode and cathode with respect to said control electrode.

2. An electron discharge device comprising a plurality of electrodes including an anode, a cathode, and a control member, an envelope having an upper and a lower section of ceramic, means sealing said anode into an aperture in said upper section, a pair of spaced ridges elevated from the surfiace of said lower section, means supporting said cathode from said lower section and between said ridges, said control member comprising a plurality of spaced wires having spring means connected to the ends of said wires applying tension thereto, said control member being stretched across said ridges, said ridges providing a reference surface and support for said member.

3. An electron discharge device comprising a plurality of electrodes including an anode, a cathode and a control member, an envelope having an upper and a lower section of ceramic, bonding means uniting said sections together, means supporting said anode and cathode with respect to said control member, said control member comprising a plurality of spaced wires, a pair of resilient bars connected to opposite ends of said wires, and means constantly urging said bars apart maintaining said control member wires at a relatively constant tension for all operating conditions of said device.

References Cited in the file of this patent UNITED STATES PATENTS 

